Acifluorfen, 5-(2-chloro-4-trifluoromethyl-phenoxy)-2-nitrobenzoic acid, and its agronomically acceptable salts are selective diphenyl ether herbicides which have both pre- and post-emergence weed control. They are particularly useful in the post-emergence control of a wide variety of broadleaf weeds. However, there are some broadleaf weeds, for example, velvetleaf and common cocklebur, against which its herbicidal activity is considered inferior. Citrate salts per se have no significant herbicidal activity.
Copending U.S. patent application Ser. No. 99,769 filed Dec. 3, 1979, abandoned, by Gerald E. Kollman, discloses the use of an aqueous composition containing a water soluble salt of an inorganic or organic acid and acifluorfen, or an agronomically acceptable salt thereof, as a means for obtaining improved weed control including the control of velvetleaf. Additionally, sodium acifluorfen has been formulated with sodium citrate dihydrate to enhance the stability of the herbicide. However, the amount of citrate added has been generally less than about half the weight percent of the sodium acifluorfen present, which is insufficient to cause any beneficial effect on the activity of the herbicide.
The present invention recognizes that compositions of acifluorfen and its agronomically acceptable salts in combination with citrate salts have a particularly pronounced effect on enhancing the herbicidal activity of the acifluorfen and in broadening the spectrum of activity particularly against velvetleaf.